1. Field of the Invention
The present invention relates to a radio communication system. More particularly, the present invention relates to a method of operating multiple time alignment timers in a Long Term Evolution (LTE) system using multiple carriers.
2. Description of the Related Art
With the rapid advance of radio communication technology, mobile communication systems have highly evolved. Long Term Evolution (LTE) is one of the promising 4th generation mobile communication technologies. In an LTE system, various techniques are adopted to meet the explosively increasing traffic demands. Carrier aggregation is one such technique. Carrier aggregation is used to flexibly expand available bandwidth by aggregating multiple secondary carriers with a primary carrier, unlike the legacy LTE system using a single carrier, between a User Equipment (UE) and an evolved Node B (eNB). In LTE, the primary carrier is referred to as Primary Cell (PCell) and the secondary carrier as Secondary Cell (SCell).
When the locations of the eNB apparatuses using the primary and secondary carriers are different from each other due to the deployment of repeaters and Remote Radio Head, it may be necessary to change the uplink transmission timing. For example, when the eNB apparatus operating with the primary carrier and another eNB apparatus operating with the secondary carrier are located at different places, it may cause a problem in transmission timing according to the location of the UE since the uplink signal to the eNB apparatus located at a further distance should be transmitted earlier than the signal to the other eNB apparatus. In this case, i.e., if there are multiple uplink timings, there is a need for managing the uplink timings efficiently.
When the locations of the eNB apparatuses using the primary and secondary carriers are different from each other due to the deployment of repeaters and Remote Radio Head, it may be necessary to change the uplink transmission timing. For example, when the eNB apparatus operating with the primary carrier and another eNB apparatus operating with the secondary carrier are located at different places, it may cause a problem in transmission timing according to the location of the UE since the uplink signal to the eNB apparatus located at a further distance should be transmitted earlier than the signal to the other eNB apparatus. In this case, i.e., if there are multiple uplink timings, there is a need for managing the uplink timings efficiently.